Method of recovering hydrocarbon fluids from a subterranean formation



sheet @f2 prll 29, 1969 B. M. FlTzGERALD METHOD OF RECOVERINGHYDROCARBON FLUIDS FROM A SUBTERRANEAN FORMATION Filed Nov. 9. 1967INVENTOR.

HTTO/P/VEV April 29, 1969 B. M. FITZGERALD 3,441,083

METHOD OF RECOVERNG HYDROCARBON FLUDS FROM A SUBTERRANEAN FORMATIONFiled Nov. 9, 1967 Sheet 2 of 2 INVENTOR.

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United States Patent O 3,441,083 METHOD OF RECOVERING HYDROCAR- BONFLUIDS FROM A SUBTERRANEAN FORMATION f Benny M. Fitzgerald, Houston,Tex., assignor to Tenneco Oil Company, Houston, Tex., a corporation ofTexas Filed Nov. 9, 1967, Ser. No. 681,655

Int. Cl. E21b 43/24 U.S. Cl. 166-245 8 Claims ABSTRACT OF THE DISCLOSUREA method of producing hydrocarbonfrom a subterranean formationcontaining crude oil, particularly a viscous type crude oil. The methodcontemplates the combination of steam drives and an in-sit combustions,

This invention relates to a method of producing hydrocarbons from asubterranean formation containing a viscous type crude oil, which methodutilizes both a steam drive technique and an in-situ combustiontechnique, in combination with a particular spacing. y

Many methods have been suggested for recoving low gravity viscous typecrude oils, including such processes as steam injection or in-situcombustion. Both processes ind application in crude oil reservoirs, butboth have limited applications by themselves in such heavy oil resetvoirs as the Athabasca Tar Sands in Canada. Steam injection has provedsuccessful in the tar sands, but the time necessary to successfullyexploit the tar makes this process limited. In-situ combustion hasproved yworkable in tar sands, but the lack of permeability and pluggingresults in inecient oxygen utilization. It is also desirable to have aspotting pattern for the wells to give the most eiicient coverage andutilization of steam and combustion.

It is therefore an object of this invention to provide a method ofrecovering heavy viscous oils from a hydrocarbon bearing formation, suchas oil-bearing sands, or shale, wherein the oil is a gravity of l6 APIor less. More specifically, the invention has application to theproduction of oil from oil bearing reservoirs containing oil 1,000 cp.,or greater, (measured at standard temperature and pressure).

Briey stated, the method of this invention contemplates drilling aplurality of production wells downwardly to bottom portions of aformation containing crude oil, with the pattern for the productionwells being in the form of a plurality of equilateral polygons having aneven number of sides. The invention also includes drilling a pluralityof steam injection wells spaced apart from the production wells andextending downwardly to bottom portions of the formation, with each ofthe Steam injection wells being spotted in the center of one of thepolygons. It also includes drilling a plurality of air injection wellsspaced apart from the steam injection wells and production wells andextending into top portions of the formation, with each of the airinjection wells being spotted substantially equal distance between twoof the production wells and on a line forming a side of one of thepolygons. Forward steam injection is performed through the bottomportion of the formation from the steam injection wells to theproduction wells. In-situ combustion is started 3,441,083 Patented Apr.29, 1969 ICC in the injection wells in top portions of the formation,which combustions are continued by supplying air under pressure throughthe air injection wells, whereby the heat of the steam injection, gavitypressure, combustion pressure, and heat causes the hydrocarbon fluids inthe oil to flow toward the production wells. Thereafter, the fluidhydrocarbons are produced from the production well.

In certain embodiments of the method, it may be necessary to fracturethe formation near the bottom thereof prior to the aforesaid steaminjection step and this fracturing may be carried out by conventionalmeans such that the fracture extends between the rst injection well andthe production well.

In certain embodiments of the invention, and prior to said forwardinjection of steam, it may be necessary to rst cyclically inject steamalternately in a steam injection well and a production well, andalternately producing the steam injection well and the production wellafter each steam injection. These alternate steam injection andproduction steps may be continued until there is communication betweenthe steam injection well and the production well through the formation,whereby the aforesaid forward steam injection step may be carried out.

It is desirable to heat the formation to at least 200 F. In certaininstances, it may be necessary to heat the formation to as high as 300F., depending upon the viscosity of the oil which is being produced.

Reference to the drawings will further explain the invention whereas:

FIG. 1 shows an ideal well pattern for a virgin reservoir, with theproduction wells ldesignated by small circles, steam injection wellsdesignated by small squares, and air injection wells designated by smalltriangles, and in which the production wells form a pattern in the shapeof an equilateral polygon in the form of a hexagon.

FIG. 2 is a schematic side elevation view of a production well, a steaminjection well and an air injection well drilled into the formationcontaining the oil to be produced.

FIG. 3 shows an alternate pattern for the wells, which pattern might beused in connection with a producing reservoir.

FIG. 4 shows still another well pattern which may be used under someconditions.

Referring now to FIGS. l and 2, the method for carrying out the presentinvention in a virgin reservoir will first be explained. Since, in avirgin reservoir, there has been no prior spacing of any productionwells, then the pattern shown in FIG. 1 is preferable because of theeconomy and coverage provided by the particular pattern shown. In otherwords, the production wells, designated by the numeral 11, are drilledin a pattern in the form of an equilateral polygon, preferably ahexagon. In the development of the eld at least one of the hexagons willhave each of its side as a common boundary for an adjacent hexagon.Production wells 11 are drilled to lower portions of formation 12 asshown in FIG. \2.

Steam injection wells, designated by the numeral 13, are also drilled toextend downward to bottom portions of the formation 12, with each of thesteam injection wells being spotted in the center of one of the polygonsformed by production well 11, as shown in FIG. 1.

Air injection wells, designated by the numeral 15, are drilleddownwardly to top portions of formation 12, with each of the airinjection wells being spotted substantially equal distance between twoproduction wells 11 and on a line forming a side of one of the polygons,`also as shown in FIG. 1.

Steam is forwardly injected from steam injection wells 13 to productionwells 11 through the lower portions of formation 12. Depending on thepermeability of the formation, it may be necessary to fracture theformation between production wells 11 and steam injection wells 13before the forward steam injection can be carried out in certaininstances. This fracturing may be carried by conventional methods, asfor example, by notching the casing in both wells at the point where thefracture is to be made and thereafter applying a fracturing fluidthereto in conventional manners, to thereby provide a fracture such asfracture 14, shown in FIG. 2, extending between a steam injection welland production well. It is to be understood that fracture 14 is locatednear the bottom of formation 12 to take full advantage of gravitydrainage.

In certain instances, and prior to the forward injecting of steamthrough the formation from wells 13 to wells 11, it may be necessary tofirst cyclically steam inject alternately in wells 13 and 11, andalternately produce wells 13 and 11 until there is communication betweenwells 13 and 11 through formation 12, as shown in FIG. 2.

The steam which is utilized for the forward steam njection is aconventional type and is generally high quality steam. The forward steaminjection is continued until at least a portion of the formation isheated to at least about 200 F. and preferably at least about 300 F.,depending upon the viscosity of the oil which is to be produced. Theheat of the steam moves upwardly through the formation by bothconvection and conduction, thereby rendering the oil less viscous andmore free flowing, such that it may be carried out to production wells11 along with the water of condensation.

When the forward steam injection has been carried on sufficiently toheat the formation to the desired temperature, in-situ combustions arestarted in the top portions of formation 12 by conventional means.Thereafter, pressurized `air is supplied downwardly through wells 15 tosustain the combustions and to generate pressure which extendsdownwardly through the formation as schematically shown in FIG. 2. Theair injection also assists in establishing gas permeability throughproduction formation 12.

The heat and pressure created by the in-situ combustions in the topportion of the formation, combined with the heat and fluid flow providedby the steam injection step, plus gravity and thermal expansion, causethe hydrocarbon fluids in formation 12 to flow downwardly in theformation where they are carried to production wells 11 along with thewater of condensation. The oil and water of condensation is thereafterproduced from wells 11 by conventional means.

Field experience has indicated that 200 F. plus temperatures arenecessary to have heavy oil sands or tar sands release their oil. Theoil does not ordinarily become mobile until these temperatures arereached. Continued temperature increase thereabove does not necessarilyproduce more oil because the energy to drive the oil from the sand intothe fracture is missing. Hence, the use of the in-situ combustion abovethe fracture in the sand accomplishes the desired result with a minimumof heating. With this combination of steps, the oil is more mobile andwill not plug the formation.

The spacing of the wells is also important to provide the optimum numberof wells to effectively cover a given area which is to be subjected tosteam injection and air injection. In the usual development of thermalrecovery projects in the past, a single well is tested first toascertain whether the formation will take steam or air. Next, a patternis drilled (usually a five-spot pattern) to pilot test the area. Fromthis point on, if the pilot is successful, development is rapid andcustomarily follows the five-spot pattern. This five-spot patternconsists of an injection well and four producing wells spacedthereabout. `If steam or air injection alone is practiced, this is anadequate pattern. However, it is not the most effective pattern for realcoverage, particularly if both air and steam injection are to be carriedon concurrently, as described above.

In the pattern of the wells in FIG. 1, which pattern is best for avirgin reservoir, each steam injection well 13 can provide steam to sixproduction wells which form the polygonal pattern, giving steaminjection patterns such as that shown by the shaded area designated bythe numeral 17. Each air injection well 15 provides an in-situcombustion extending to at least two adjacent production wells 11 andtow adjacent steam injection wells 13 and form air injection patternssuch as that shown as the shaded area designated by the numeral 18. Asstated above, each of the air injection wells 13 is spaced substantiallyequal distance between two production wells 11 and on a line forming aside of one of said polygons.

FIG. 3 shows an alternate pattern for the wells which might be used inan established producing eld where the established production wells areshown as small circles designated by the numeral 20, with additionalfill in production wells shown as black dots designated by the numeral21. It will be noted that the production wells 20 and fill in wells 21combine to form the aforesaid polygonal pattern. In the conventionaldevelopment of fields and without the use of secondary recovery, wells20 are normally drilled in straight rows, as shown in FIG. 3. When itbecomes desirable to practice the method of the present invention, thefill in wells 21 are drilled along with steam injection wells 22 and airinjection wells 23. As with the prior embodiment, each of the steaminjection wells 22 is drilled centrally in a hexagon pattern formed bythe production wells 20 and 21, and an air injection well 23 is drilledsubstantially equal distance between two 'production wells 20 and on aline forming a side of a polygon. The result is that there is providedsteam injection patterns such as that shown by the shaded areadesignated bythe numeral 24 which is substantially the same as the steaminjection patterns 17 shown in FIG. 1. Similarly, there are provided airinjection patterns designated by the numeral 25 which correspond withair injection patterns 18 in FIG. 1. One disadvantage of this patternover that described with respect to FIG. l is that no more than twosides of each hexagon form common boundaries with adjacent hexagons. Theresult is that there is provided what is some time referred to as awasted diamond shaped area between the rows of hexagon patterns asshown, which areas are not fully covered by steam and air.

Referring now to FIG. 4, an alternate and somewhat less preferredpattern for the wells is shown wherein the pattern formed by theproduction wells is in the shape of a plurality of squares. This patternmight be used, for example, where it was not possible or desirable touse the hexagonal pattern for the production wells. In this embodiment,the production wells are designated by the numeral 29, the steaminjection wells by the numeral 30 and the air injection wells lby thenumeral 31. A steam injection pattern for each steam injection well 30is shown as a shaded area designated by the numeral 33, for example.Similarly, each air injection well 31 covers an air injection patternsuch as that shown :by shaded area designated by the numeral 34. Thispattern is somewhat less efficient than the FIG. 3 embodiment andconsiderably less efficient that the FIG. 1 embodiment for the reasonthat fewer production wells are covered per steam injection well and airinjection well.

Thus, the invention provides a novel `method of producing a formationwhich combines the advantages of combustion and steam injection in-combination with a very efficient spacing pattern to accomplish optimumrecovery of otherwise unrecoverable viscous type oils.

Further modifications may be made in the invention as described withoutdeparting from the scope thereof. Accordingly, the foregoing descriptionis to be construed as illustratively only and is not to be construed asa limitation upon the invention as defined in the following claims.

What is claimed is:

1. The method of producing uid hydrocarbons from a subterraneousformation containing crude oil, said method comprising in combinationthe steps of:

drilling a plurality of production wells 4downwardly to bottom portionsof said formations, with the pattern for said production well being inthe form of a plurality of equilateral polygons having an even number ofsides;

drilling a plurality of steam injection wells spaced apart from saidproduction wells and extending downwardto bot-tom portions of saidformations, with each of said steam injection wells being spotted in thecenter of one of said polygons;

drilling a plurality of air injection wells spaced apart from said steaminjection wells and said production wells and extending downwardlyI intotop portions of said formations, with each of Usaid air,injection wellsbeing spotted substantially equal distance between two of saidproduction wells and on a line forming a side of one of said polygons;

forward injecting steam through bottom portions of said formation fromsaid steam'injection wells to said production wells;

starting in-situ combustions in said air injection wells in top portionsof said formations and continuing said insitu combustions by supplyingaifr under pressure through said air injection wells,"to thereby createdownward pressure on said oil in said formation, whereby the heat ofsaid steam injection, gravity pressure, and combustion pressure'causesthe hydrocarbon uids of said oil to flow toward said productin Wells;

andrproducing said uid hydrocarbons from said production wells.

2. The method as claimed in claim 1 including:

fracturing said formation near the bottom thereof prior toinjection ofsaid steam. y

3. Iillhe method as claimed in claim 1 including:

prior to said forward injecting of steam through said formation, firstcyclically steam injecting alternatively in one of said steam injectionwell and one of said production well and alternatively producing saidone steam injection well and said one production well after each steaminjection;

continuing said cyclical steam injection and production steps untilthere is communication between said one steam injection well and saidone production well through said formation.

4. The method as claimed in claim 1 including:

continuing said forward steam injection until at least a portion of saidformation is heated to at least 300 F.

5. The invention as claimed in claim 1 wherein:

said polygons in said pattern are hexagons.

6. The invention as claimed in claim 5 wherein:

each side of at least one of said heXagons forms a common boundary ofanother hexagon.

7. The invention as claimed in claim 5 wherein:

no more than two sides of each hexagon form common boundaries withadjacent hexagons.

8. The invention as claimed in claim 1 wherein:

said polygons in'said pattern are squares.

References Cited UNITED STATES PATENTS 3,000,441 9/ 1961 Kunetka 166-113,048,221 8/1962 Tek 166-11 3,120,870 2/ 1964 Santourian 166-9 3,129,7584/1964 Closmann 166-11 3,316,962 5/ 1967 Lange 16611 3,358,754 12/1967Stelzer et al. 166-2 3,358,759 12/1967 Parker 166-11 3,380,527 4/1968Craighead 166-11 3,384,172 5/1968 Hujsak et al 166-11 3,385,361 5/1968Terwilliger 166-11 STEPHEN J. NOVOSAD, Primary Examiner.

U.S. Cl. X.R.

